The present invention relates to improvement in electric discharge machining method and apparatus in which a machining condition can be set by use of graphic data of a tool electrode or a subject for machining generated by CAD or the like.
In electric discharge machining, a machining condition, an oscillating condition, etc. to be set are determined in accordance with the shape of a tool electrode and electric discharge energy at the time of machining. For example, a high-energy machining condition is used in rough machining and a low-energy machining condition is used in final machining for selecting an oscillating condition to make the shape of a subject for machining analogous to the shape of the tool electrode in accordance with the target machining shape of the subject.
The machining condition used in rough machining is determined in accordance with the expected shape of the subject, the depth of machining, the number of tool electrodes used in machining and the scaling-down margin as the downsizing quantity for the final shape and the tool electrode. The machining condition used in final machining is determined in accordance with target accuracy in the final machining shape of the subject, surface roughness and the degree of abrasion of the tool electrode. With respect to the oscillating condition, the relative movement between the tool electrode and the subject is controlled to obtain quadrilateral or polygonal oscillation when angularity of the final machining shape of the subject is regarded as important, and the relative movement between the tool electrode and the subject is controlled to obtain circular-arc, elliptic or spherical oscillation when the final machining shape of the subject has roundness.
Further, in the case where the area of machining at an initial stage of machining is so small that abrasion of the tool electrode becomes intensive when machining is performed under a rough machining condition, control, so-called lead-in control is performed so that machining is started under a low-energy machining condition before the machining condition is gradually changed to an original rough machining condition. Further, adaptive control or the like for discharge interrupt time, jump motion, etc. is performed.
In this manner, lots of machining conditions must be set for electric discharge machining. Moreover, these machining conditions strongly depend on the shape of the tool electrode and the aimed machining content. Hence, technical skill is required for setting the machining conditions.
To solve this problem, Japanese Patent Laid-Open No. 218517/1990 has disclosed an electric discharge machining method and apparatus in which an operating person inputs information concerning materials of a tool electrode and a subject for machining to be used, maximum machining area at the time of rough machining and surface roughness at final machining so that optimal electrical conditions and optimal oscillation quantities at multistage oscillation machining are obtained by calculation based on the input information.
On the other hand, Japanese Patent Laid-Open No. 178731/1991 has disclosed an electric discharge machining apparatus in which a tool electrode shape sensor provided in a machining tank is used or tool electrode shape information in an NC program is used so that machining is performed while machining conditions optimal for the case where the state is replaced by a state of actual electric discharge machining are automatically selected.
In the electric discharge machining method and apparatus disclosed in Japanese Patent Laid-Open No. 218517/1990, there was a problem that it was necessary to generate a function for recognizing the area of machining and a machining condition corresponding to the machining area when the shape of machining was complex because the electric discharge machining apparatus could not recognize three-dimensional information of the tool electrode and the machining shape of the subject when the machining content was input.
On the other hand, in the electric discharge machining apparatus disclosed in Japanese Patent Laid-Open No. 178731/1991, graphic data of a tool electrode generated by CAD or the like is used for generating machining conditions. However, shape data original to the graphic data is not effectively used but only information of surface area per unit height of a tool electrode having a three-dimensional shape generated by CAD/CAM is used. Further, no disclosure has been made on the method, etc., for performing controlling over machining done by a complex-shape tool electrode, and for generating machining conditions.
The present invention is designed to solve the aforementioned problems and an object of the invention is to provide an electric discharge machining method and apparatus in which efficient machining can be performed even in the case where the shape of machining is complex.
The electric discharge machining method according to the invention is an electric discharge machining method for performing machining under a machining condition selected while making either of shape information of a tool electrode and shape information of a subject for machining correspond to machining condition data in a machining condition database, having: a first step of reading either of shape data of the tool electrode and machining shape data of the subject; a second step of extracting either of shape characteristic of the tool electrode and machining shape characteristic of the subject from the shape data; and a third step of performing machining under a machining condition selected while making either of the shape characteristic of the tool electrode and the machining shape characteristic of the subject correspond to machining condition data in the machining condition database.
Further, the electric discharge machining method according to the invention is an electric discharge machining method for performing machining under a machining condition selected while making either of shape information of a tool electrode and shape information of a subject for machining correspond to machining condition data in a machining condition database, having: a first step of reading either of shape data of the tool electrode and machining shape data of the subject; a second step of extracting a plurality of sections from the shape data; a third step of mesh-dividing the sections and giving mesh data of solidness or hollowness; a fourth step of extracting either of shape characteristic of the tool electrode and machining shape characteristic of the subject from the mesh data; and a fifth step of performing machining under a machining condition selected while making either of the shape characteristic of the tool electrode and the machining shape characteristic of the subject correspond to machining condition data in the machining condition database.
Further, in the electric discharge machining method according to the invention, the most frequent shape characteristic obtained in either of shape characteristic information of the tool electrode and machining shape characteristic information of the subject on the basis of the mesh data is recognized as either of shape characteristic of the tool electrode and machining shape characteristic of the subject.
The electric discharge machining apparatus according to the invention is an electric discharge machining apparatus having machining condition storage means including a machining condition database in which a plurality of pieces of machining condition data are stored, wherein the electric discharge machining apparatus further has: input means for reading either of shape data of a tool electrode and machining shape data of a subject for machining; shape computing means for extracting a plurality of sections from the shape data, mesh-dividing the sections into split elements, giving mesh data of solidness or hollowness to each of the split elements and extracting either of shape characteristic of the tool electrode and machining shape characteristic of the subject from the mesh data; and machining condition setting means for selecting a machining condition while making either of the shape characteristic of the tool electrode and the machining shape characteristic of the subject correspond to machining condition data in the machining condition database of the machining condition storage means.
Further, in the electric discharge machining apparatus according to the invention, the most frequent shape characteristic obtained in either of shape characteristic information of the tool electrode and machining shape characteristic information of the subject on the basis of the mesh data is recognized as either of shape characteristic of the tool electrode and machining shape characteristic of the subject.
Because the invention is configured as described above, machining shape characteristic can be extracted so that an appropriate machining condition can be set by use of more detailed shape information. Hence, there is an effect that more efficient machining can be performed even in the case where the machining shape is complex.